The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus including the electrophotographic photosensitive member.
As photoconductor materials for electrophotographic photosensitive members, inorganic photoconductors, such as cadmium sulfide, and zinc oxide, have been conventionally used. On the other hand, organic photoconductors, such as polyvinyl carbazole, oxadiazole, azo pigments and phthalocyanine have advantages of a non-pollution characteristic and high productivity compared with inorganic photoconductors but generally have a low conductivity so that the commercialization thereof has been difficult. For this reason, various sensitizing methods have been proposed, and among them, the use of a tunction separation-type photosensitive member including a charge generation layer and a charge transport layer in a laminated state has become predominant and have been commercialized.
On the other hand, in recent years, non-impact-type printers utilizing electrophotography have come into wide use in place of conventional impact-type printers as terminal printers. Such non-impact-type printers principally comprise laser beam printers using laser light as exposure light, and as the light source thereof, semiconductor lasers have been predominantly used, in view of the cost and apparatus size thereof. The semiconductor lasers principally used currently have an oscillating wavelength in a long wavelength region of 650-820 nm, so that electrophotographic photosensitive members having a sufficient sensitivity in such a long wavelength region have been developed.
Azo pigments and phthalocyanine pigments are very effective charge-generating materials having a sensitivity up to such a long wavelength region. Azo pigments are disclosed in, e.g., Japanese Laid-Open Patent Application (JP-A) 59-31962 and JP-A 1-183663. Further, compared with conventional phthalocyanine pigments, oxytitanium phthalocyanine and gallium phthalocyanine are known to have better sensitivities, and various- crystal forms thereof have been disclosed, e.g., in JP-A 61-239248, JP-A 61-217050, JP-A 62-67094, JP-A 63-218768, JP-A 64-17066, JP-A 5-98181, JP-A 5-263007 and JP-A 10-67946. Further, JP-A 7-128888 and JP-A 9-34149 have disclosed a combination of a specific azo pigment with a phthalocyanine pigment for providing improvements to problems accompanying such a phthalocyanine pigment. However, it is still desired to develop a photosensitive member capable of providing images free from image defects to a greater extent while retaining a high sensitivity characteristic.
While having such an excellent sensitivity characteristic, an electrophotographic photosensitive member using an azo pigment or a phthalocyanine pigment is accompanied by the difficulty that generated photocarriers are liable to remain in the photosensitive layer, thus functioning as a memory for causing a potential fluctuation. While the mechanism or principle thereof has not been fully confirmed or clarified as yet, it is assumed that the above difficulty is caused by the phenomenon that electrons left in the charge generation layer move for some reason to the boundary between the charge generation layer and the charge transport layer, or the boundary between the charge generation layer and the undercoating layer or the undercoating layer and an electroconductive layer therebelow, thereby increasing or decreasing the barrier characteristic against hole injection in the vicinity of the boundaries.
As actual phenomena occurring in electrophotographic photosensitive members, electrons remaining at the boundary between the charge generation layer and the charge transport layer result in a lowering in light-part potential or dark-part potential during continuous image formation. For example, in the so-called reversal development system frequently adopted in printers at present wherein a light-potential portion is developed with toner as an image portion while a dark-potential portion is left as a non-image portion, a portion of photosensitive member exposed in a previous printing cycle is caused to reach a light-part potential at a lower exposure quantity and is developed as a black ghost image in a white solid image area in a subsequent printing cycle, thus causing a noticeable ghost phenomenon (hereinafter called a xe2x80x9cpositive ghostxe2x80x9d).
On the other hand, electrons remaining at the boundary between the charge generation layer and the undercoating layer or between the undercoating layer and the electroconductive layer therebelow result in an increase (or an insufficient lowering) in light-part potential. When such a photosensitive member is used in the reversal development system, a portion of the photosensitive member exposed in a previous printing cycle is developed at a slower speed and is developed as a white ghost image in a back solid image area in a subsequent printing cycle, thus causing a noticeable ghost phenomenon (hereinafter called a negative ghostxe2x80x9d).
Among the above ghost phenomena, the negative ghost is liable to occur in an initial stage and the positive ghost is liable to occur in a later stage in a continuous printing operation (image formation). These ghost phenomena are noticeably observed especially in a photosensitive member including an undercoating adhesive layer for the charge generation layer and are particularly liable to occur in a low temperature/low humidity environment wherein the volume resistivity for electron movement in the charge generation layer and the undercoating layer is liable to increase so that the electrons are liable to remain abundantly in the charge generation layer.
An object of the present invention is to provide an electrophotographic photosensitive member capable of forming images free from image defects while retaining a high sensitivity, particularly in a semiconductor laser wavelength region.
Another object of the present invention is to provide a process cartridge and an electrophotographic apparatus including an electrophotographic photosensitive member as mentioned above.
According to the present invention, there is provided an electrophotographic photosensitive member, comprising a support and a photosensitive layer disposed on the support, wherein said photosensitive layer contains an azo calix[n]arene compound represented by the formula (1) below: 
wherein n denotes an integer of 4-8; a number (n) of R1 independently denote a hydrogen atom or an alkyl group capable of having a substituent and including at least one alkyl group capable of having a substituent; a number (2n) of R2 independently denote a hydrogen atom or an alkyl group capable of having a substituent; and a number (n) of Ar independently denote a monovalent group selected from an aromatic hydrocarbon ring group capable of having a substituent, a heterocyclic ring group capable of having a substituent, and a combination of these groups capable of having a substituent.
The present invention further provides a process cartridge and an electrophotographic apparatus including the electrophotographic photosensitive member.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.